Organopolysiloxanes and organosilanes have for some time been used to improve certain electrical properties or to provide new attributes in electrical insulations comprising ethylene-containing polymeric compositions filled with clay. Note, for example, U.S. Pat. Nos. 3,148,169; 3,795,646; and 3,802,913, and a technical paper entitled: "The Effect Of Silane Coupling Agents In Improving The Properties Of Filled Or Reinforced Thermoplastic" by Sterman and Marsden, published by the Society of Plastics Engineers, Inc., Technical Papers, Volume XI, 21st annual technical conference, Mar. 1 - Mar. 4, 1965.
These organic silicon compounds are generally included in such electrical insulating materials for the purpose of overcoming the effects of moisture and/or clays which adversely influence the electrical properties and electrical insulating performance of polymeric compositions.
However, in the higher voltage carrying transmission cables such as about 5 KV and above, it has been necessary to subject newly produced insulated cable products to a prolonged "ovenizing" or high temperature treatment to achieve an acceptable low power factor of about 0.75% or less, regardless of the presence of significant amounts of such organopolysiloxanes or organosilanes.
Ovenizing or heat treating comprises the traditional means for enhancing electrical properties in polymeric insulations for high voltage service. This treatment reduces the water contents of the insulating materials which, among other possible sources, results from the conventional use of high pressure sources, results from the conventional use of high pressure steam for the curing of thermosetting insulations or other components of the cable covering.